A cataract is the clouding of the natural lens of the eye. In decades past, persons affected with cataracts were treated by removing the cataractous lens tissue and after a suitable recovery period, fitting the patient with thick glasses. While such glasses were conventionally worn, they were often distinctly unconventional in appearance. Some critics describe them as having a thickness approximating that of the bottom of a soft drink bottle. They caused a great deal of distortion to a patients vision.
A relatively recent (and more informed) treatment involves implantation of an artificial intraocular lens (IOL) into the eye after the removal of the cataractous natural lens. The natural lens of the eye is a convex lens which is thicker in the center and thinner on the edges. The IOLs used to replace the natural lens are likewise convex lens which are thicker in the center and thinner on the edges. The thickness varies depending upon the power of the lens and the index of refraction of the material used to produce it. IOLs of the same power can be manufactured with the convexity entirely on one side of the lens or split in various combinations between the two sides. IOLs consist of two basic parts: the "optic" portion which bends the light to produce the focusing power of the lens, and the "haptic" which is the non-optical carrier portion supporting the IOL in the eye. The optic portion of IOLs are usually circular or elliptical. The haptic portions have been produced with a very wide variety of shapes and configurations.
Older cataract extraction techniques involve the removal of the clouded natural lens as a whole or in large pieces. This necessitates a relatively long (perhaps 10 mm or more) incision through the wall of the eye. Commonly such an incision is a "plunge" wound, the depth of which is generally perpendicular to the eyeball wall. Such procedures are characterized by a number of disadvantages. Large incisions require sutures, cause discomfort and have a long healing time before return to normal activities.
Another now commonly used technique for cataract extraction is by phacoemulsification which uses ultrasonic vibration fragmentation and aspiration. This allows the removal of the cataract through a small incision only about 3 mm long.
The IOLs which were first developed were made of hard materials with optics about 6 mm in diameter. These, of course, require incisions for insertion which are at least about equal to the diameter of the IOL. These lenses were well suited for the older technique of cataract extraction which required larger incisions, but not well suited for the smaller incisions used in the phacoemulsification technique.
More recently, the soft foldable silicone artificial intraocular lens was developed. This permits a lens with an optical portion about 6 mm in diameter to be folded in half and inserted in the eye. This allows the insertion to be performed through a small incision which is about half as long as the diameter of the unfolded lens. After the folded soft IOL is inserted in the eye, it is permitted to unfold to its full diameter. Such a lens is well suited to be used after the cataract is extracted by the phacoemulsification technique which is done through a small incision.
The techniques of removing a cataract and implanting an IOL through small incisions has a number of advantages for the patient. There is less discomfort from the surgery, faster healing and a more rapid return to normal activities.
The most recent development in cataract surgery includes forming an incision or path to the interior of the eye which differs from previous practice. Instead of forming a "straight line" path to the interior of the eye, the wound is formed tunnel-fashion along three relatively distinct segments. The first is from the outer surface of the eye inward to a depth of about one-half the thickness of the eyeball wall and generally perpendicular to it. The second segment is generally parallel to the interior and exterior eyeball walls and about midway between them. The third segment is also normal to the walls of the eye and enters the eye interior. If viewed in cross section, the wound may be said to have three segments of incision forming a "double-step" path. These wounds are known as "scleral tunnel" incisions. Using a wound of this type for lens implantation results in an advantage for the patient. When the eyeball is slightly pressurized by the surgeon, the wound is self sealing. As a result, sutures can be avoided.
Small incision and tunnel-like wounds have required new instruments and surgical techniques for lens implantation. In the vernacular, such wound configuration requires the surgeon to work in very close quarters.
Several relatively new techniques and instruments have been developed to accommodate wounds of reduced width. For example, the issue of Ocular Surgery News of Jul. 15, 1990 discusses a cryo device which is said to freeze a foldable IOL for insertion through a small incision.
Another type of instrument, referred to as a lens injector or "shooter," is shown in catalog sheets published by Staar Surgical Company. The injector rolls a soft lens into a barrel or tube and expels it syringe-style into the interior after the instrument is inserted into the eye. Loss of control is said to be a disadvantage of instruments of this type.
U.S. Pat. No. 4,759,359 (Willis et al.) shows what has come to be known as the phaco-folder. The Willis et al. instrument has a curved trough into which a soft IOL is forced and folded along a diameter by a wire-like end. The trough and the end can be manipulated toward and away from one another.
The instrument shown in U.S. Pat. No. 4,785,810 (Baccala et al.) is similar in concept to that shown in the Willis et al. patent. However, it is illustrated in connection with a soft IOL having an elongate shape and integrally molded tang-like haptics.
These instruments share two disadvantages. One is that the surface of the lens which faces outward upon implantation is interior when the lens is folded. It has been found that in a preferred soft IOL fold, such surface should be exterior. Another is that both instruments include portions (a trough or jaw means as identified respectively in such patents) which increase the thickness of the lens-instrument combination precisely in that region where such an increase is least tolerated. To put it another way, the Willis et al. and Baccala et al. instruments have portions adjacent to the relatively thick lens center or optical portion when the lens is folded and inserted. This disadvantage is aggravated with IOLs of increasing diopter power since such IOLs are thicker at their center optical portion -- and therefore thicker along a diameter fold line.
U.S. Pat. No. 4,844,065 (Faulkner) describes an inserting tool having a pair of relatively straight jaws for holding a circular lens which is folded. Such jaws are bowed outward slightly to accommodate lens curvature and engage the lens along a geometric chord where the lens is somewhat thinner than at its center -- but significantly thicker than at the lens edge. The Faulkner tool undesirably adds to the overall thickness of the instrument-lens combination.
A new instrument for implanting a soft IOL which avoids increasing the thickness of the IOL-instrument combination, which can be used with narrow incisions including scleral tunnel incisions and which permits good control of the IOL being released into the eye would be an important advance in the art.